1. Field of the Invention
The present invention relates to a system comprising a series of data carriers, in particular identity cards, papers of value or the like, whereby the data carriers belonging to the system exhibit diffraction structures containing standard information, to such data carriers and to methods for producing them.
2. Discussion of Related Technology
Optically variable elements have been known in various embodiments for some decades. These elements have in common that they show different optical effects depending on the angles of viewing and illumination. One particular class of optically variable elements is based on diffractive effects. It includes linear or structured diffraction grids, holographic recordings, cinegrams and the like.
Optically variable elements are employed in a great variety of areas, e.g. in advertising, decorating, but also for marking the authenticity of data carriers. Due to their optical quality that has considerably increased in the past while, holograms, cinegrams, diffraction grids, etc., are being increasingly used in the security field, for example for credit cards, identity cards, bank notes, security documents, etc. The rise in popularity is essentially due to two circumstances. Firstly, such elements meet the traditional security requirements for humanly testable authenticity features, i.e. high expenditure for production and imitation, poor availability of the technology and unambiguous testability without additional aids. Secondly, the elements are based on the newest state of the art so that they give the corresponding product a modern, high-tech character.
In the patent literature and in their practical application in the security field, such elements have become known up to now in various versions.
Very soon after the appearance of the first holograms the proposal was made to protect identity cards, credit cards and the like from imitation and falsification by storing the card user's personal data not only in the customary photographic and/or written form but also holographically in a hologram on the card. A comparison between the conventional card data and the data stored in the hologram was intended to prove their correctness. Of the many relevant publications, German “offenlegungsschrifts” nos. 25 01 604, 25 12 550 and 25 45 799 are stated by way of example.
Although the traditional security philosophy requires the expenditure for producing authenticity features to be high, this holds primarily for the original value and the poor availability of the necessary production equipment. The production of the authenticity features themselves, which are to be produced in large amounts, should nevertheless be economical on this relatively expensive production equipment.
With various types of hologram, the preparation of the first hologram is relatively troublesome and expensive. However, it is possible to produce duplicates at a fraction of this “first cost.”
Such embodiments thus prove to be disadvantageous not only because the holograms must be produced on very expensive technical equipment but also because separate holograms with individual information (personalization data) must be produced for each card, so that the technical effort for preparing these individual holograms (unicates) is always relatively high. The cost can be reduced only minimally by shifting the effort to the production apparatus. Due to these detrimental marginal conditions the use of holograms with holographically stored card-specific data is unreasonable from a financial point of view.
Different techniques are used depending on the type of data carrier or of holographic standard element. Without laying any claim to completeness one can state the following:                directly embossing the hologram structure on the recording medium which has a suitable surface quality, e.g. on plastics materials,        heat-sealing or gluing a hologram provided on an intermediate carrier onto the recording medium itself, which may have a paper or plastics surface, e.g. bank note, paper of value, identity card, etc.,        laminating or mounting a hologram provided on an intermediate carrier into the interior of a multilayer recording medium,        embedding safeguarding threads or planchets with holographic diffraction structures in paper during the paper production process.        
The process most frequently used today for producing and applying standard holograms to data carriers is the transfer of embossed holograms to identity cards. For this reason the production process and the individualizing measures shall be presented by way of example with reference to this technology. The essential method steps are the preparation of a master hologram, the production of hologram copies and the application to the subsequent product.
The master is generally prepared by manual single-piece production with very expensive equipment. The master hologram therefore involves high cost. The copies can be produced and applied to the cover foils of the cards automatically at high speed and thus at relatively low cost. Due to this cost structure one endeavors to minimize the fixed cost per hologram by preparing a maximum number of identical copies. The necessity of mass production thus leads in the security field, in particular in the card branch, to restrictions with respect to the holographic protection against forgery.
To reduce the cost of producing the hologram, embodiments have become known in which holograms are used as an authenticity feature but the data stored in the hologram are not individualized for the user but merely exhibit an individuality relating to the card issuer (standard holograms). The holograms of different card systems differ from each other, but the holograms of the individual cards of a system are identical.
By using standard holograms (i.e. duplicates of a master hologram) for a card system it now became possible to distribute the relatively high fixed cost for the holographic recording technique over a high number of cards. Depending on the extent of the card series, the cost may thus be distributed over such high piece numbers that virtually only the duplication cost shows in the books for the price of the individual hologram. This fact made holograms economically feasible as mass-produced articles in the security field for the first time.
Along with the well-known applications in the Eurocheck system and for VISA and Mastercard credit cards, examples of these various applications are German “offenlegungsschrift” no. 33 08 831 and European patent no. 0 064 067.
The holograms used in current credit card systems are known to be so-called “embossed holograms,” which allow for reproduction by means of die-plates. Although a major part of the production cost arises for the holographic recording technique, the cost to be calculated for reproducing the holograms in series production is still so high that an economical production is only possible if the necessary cost for the recording technique and the production of the hologram master can be apportioned among series with many millions of pieces. The production of small lots, i.e. a few ten thousands to one hundred thousand cards, is usually still impossible for financial or economic reasons.
When using like holograms within a card series one can make cards of one system differ better from cards of another; but the falsification of cards is not fully excluded since such holograms can still be punched out and transferred to other cards. Measures exist for making such manipulation more difficult by shifting the embossed data relating to the card user partly or completely to the hologram area. But it is well-known that the embossed data can be reembossed, whereby such manipulation is recognizable in practice only for experts, and not for laymen. The provision of card-specific embossed data in the area of the standard hologram thus fails to offer genuine protection from a transferral to other cards.
To avoid such problems Austrian patent no. 334 117 describes the application of standard holograms to the user-related individualization of cards. According to this proposal the card individualization is permitted by the combination of several standard holograms each containing certain information of its own, e.g. letters or numbers, and representing different data, such as words, multidigit numbers, etc., through a corresponding combination on the individual cards of a system. By embossing such holograms with the aid of a standard set of press dies one obtains a simple and inexpensive production of individual holographic card data.
However, since alphanumeric data are mainly applied to this variant and particularly pictorial data cannot be readily reproduced, the overall impression of such holograms is visually not very effective, which is why this form of individualization has not gained much acceptance on the market up to now.
A further variant for individualizing documents using holograms is described in German “offenlegungsschrift” no. 25 55 214. Here, it is proposed that diffraction structures in the form of numerical or alphanumeric characters be applied to a document. A thermoplastic ink is printed in the form of numbers on a paper substrate, whereafter the diffraction structure is embossed with a large-surface die.
However, this variant is unsuitable for multilayer types of hologram, which are particularly preferred for producing data carriers since the diffraction structure is located inside and is thus protected.
The prior art shows that the existing needs in security technology and the feasibility of economically reasonable solutions have not yet found a common denominator.
Assuming this general view and the related prior art, the invention is therefore based on the problem of proposing diffraction-structure elements, and in particular hologram variants and production methods for them, that allow for a degree of individualization of the holograms adapted to the particular security aspects, and thus for maximum protection of the data and documents, while at the same time offering the cost advantages of the series production of standard holograms.